It is known that lubricants become less effective during their use due to exposure to the operating conditions of the device they are used in, and particularly due to exposure to by-products generated by the operation of the device. For example, engine oil becomes less effective during its use, in part due to exposure of the oil to acidic and pro-oxidant byproducts. These byproducts result from the incomplete combustion of fuel in devices such as internal combustion engines, which utilize the oil. These byproducts lead to deleterious effects in the engine oil, and so, on the engine as well. The byproducts can oxidize hydrocarbons found in the lubricating oil, yielding carboxylic acids and other oxygenates. These oxidized and acidic hydrocarbons can then go on to cause corrosion, wear and deposit problems.
Base-containing additives are added to lubricants in order to neutralize such byproducts, thus reducing the harm they cause to the lubricant, such as an engine oil, and so to the device, such as an engine. Over-based calcium or magnesium carbonate detergents have been used for some time as acid scavengers, neutralizing these byproducts and so protecting both the lubricant and the device. However, over-based phenate and sulfonate detergents carry with them an abundance of metal as measured by sulfated ash (ASTM D 874). New industry upgrades for diesel and passenger car lubricating oils are putting ever decreasing limits on the amount of sulfated ash, and by extension the amount of over-based detergent, permissible in an oil.
There is a need for additives that can extend the operational effectiveness of base-containing additives without the addition of increased sulfated ash. In particular, there is a need for additives that can improve the retention of basicity in a lubricant while continuing to minimize the effects of acid build-up in the lubricant.
U.S. Pat. No. 2,390,943 (Kavanagh et al., Dec. 11, 1945) relates to compositions comprising hydrocarbon oil and a combination of stabilizing ingredients.
U.S. Pat. No. 2,369,090 (Trautman, Feb. 6, 1945) and U.S. Pat. No. 3,856,690 (Milton, Dec. 24, 1974) relate to lubricants which are stabilized against oxidative degradation.
U.S. Pat. No. 3,642,632 (Coburn et al., Feb. 15, 1972) relates to lubricant compositions having improved resistance to deterioration under high performance conditions.
U.S. Pat. No. 2,771,368 (Thompson, Nov. 20, 1956) relates to the use of N-substituted trialkoxy anilines as stabilizers for organic compounds, including fuels, mineral oils, and lubricating oils.
U.S. Pat. No. 4,234,434 (Wulfers, Feb. 14, 1979) relates to the use of dialkylanilines as stabilizers for hydrocracked oil.
WO/PCT application 2010/107882 (Preston et al., Sep. 23, 2010), relates to the use of anthranilic acid derivatives as ash-free amine-derived sources of basicity that do not cause harm to seals.
United States application 2010/0160195 (Cheng et al., Jun. 24, 2010) relates to lubricating compositions comprising derivatives of N,N-dialkylated aniline as ash-free boosters of total base number (TBN).
The use of phenyl-α-naphthylamines (PANA) and derivatives thereof as antioxidants in lubricating compositions is well documented. U.S. Pat. No. 3,414,618 (Randell, Dec. 3, 1968) relates to a process to produce alkylated PANA and its use as an antioxidant in lubricating compositions. Recent publications include European patent application 2055763 (May 6, 2009), which relates to a lubricating composition comprising the combination of alkylated diphenylamine and alkylated PANA, and United States application 2010/0099589 (Ryan et al., Apr. 22, 2010), which relates to a lubricating composition with a combination of alkylated PANA and triazoles for oxidation control.
Diaromatic amine antioxidants with edge-sharing rings have been described previously in United States patent applications 2009/0131293 (Ma et al., May 21, 2009) and 2009/0131290 (Ma et al., May 21, 2009). Application 2009/0131290 relates to dihydroacridan derivatives as ashless antioxidants.
It has now been discovered that lubricating compositions comprising a combination of select diarylamines with aminobenzenes, including anthranilic acid, provide for improved TBN retention. Unexpectedly, this may be accomplished without increasing the deleterious effects of acid build-up in lubricants such as engine oil.